Trajectory optimization using a combination of direct multiple shooting and collocation

Abstract

In the framework of the software package GESOP (Graphical Environment for Simulation and Optimization), a new optimization method is developed. It is a combination of a direct multiple-shooting method and a direct collocation method. For multiphase problems, the transcription can be different in each phase. Within a multiple-shooting phase, several different integration methods can be selected, ranging from second order to seventh order methods. A collocation phase is using either third order Hermite polynomials or a trapezoidal approximation. The new optimization method is developed in the object oriented programming language Ada95. Only the core NLP solver SNOPT 5.3 is written in FORTRAN and accessed via the Ada95/FORTRAN interface. User supplied models for optimization can either be written in Ada95 or FORTRAN. Since the new optimization method is fully compatible to the GESOP model interface, a large variety of models was available for testing purposes. The new method is compared with the existing GESOP optimizers PROMIS and TROPIC. All tests presented in this paper are using the complex ASTOS model (AeroSpace Trajectory Optmization Software), which is a completely data driven library designed for analysis of launcher and reentry missions.